samples: cpp: add a Hello, world! C++ app

Create a separate hello world C++ app for Zephyr.

Signed-off-by: Christopher Friedt <cfriedt@meta.com>

samples/cpp/hello_world/CMakeLists.txt

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+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.20.0)
+
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(hello_cpp_world)
+
+target_sources(app PRIVATE src/main.cpp)

samples/cpp/hello_world/README.rst

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+.. _hello_cpp_world:
+
+Hello C++ World
+###############
+
+Overview
+********
+
+A simple :ref:`C++ <language_cpp>` sample that can be used with many supported board and prints
+"Hello, C++ world!" to the console.
+
+Building and Running
+********************
+
+This configuration can be built and executed on QEMU as follows:
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/cpp/hello_world
+   :host-os: unix
+   :board: qemu_riscv32
+   :goals: run
+   :compact:
+
+To build for another board, change "qemu_riscv32" above to that board's name.
+
+Sample Output
+=============
+
+.. code-block:: console
+
+    Hello C++, world! qemu_riscv32
+
+Exit QEMU by pressing :kbd:`CTRL+C`

samples/cpp/hello_world/prj.conf

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+CONFIG_CPP=y
+CONFIG_REQUIRES_FULL_LIBCPP=y

samples/cpp/hello_world/sample.yaml

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+sample:
+  description: Hello World C++ sample, the simplest C++ Zephyr application
+  name: hello cpp world
+common:
+  tags: introduction
+  integration_platforms:
+    - qemu_riscv32
+  harness: console
+  harness_config:
+    type: one_line
+    regex:
+      - "Hello, C\\+\\+ world! (.*)"
+tests:
+  sample.cpp.helloworld:
+    min_ram: 128
+    arch_exclude:
+      # See #66027
+      - xtensa
+    platform_exclude:
+      # See zephyrproject-rtos/sdk-ng#593
+      - qemu_x86
+      - intel_ish_5_4_1
+      - intel_ish_5_6_0
+      - intel_ish_5_8_0

samples/cpp/hello_world/src/main.cpp

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+/*
+ * Copyright (c) 2023, Meta
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <iostream>
+
+int main(void)
+{
+	std::cout << "Hello, C++ world! " << CONFIG_BOARD << std::endl;
+	return 0;
+}